1. Field of the Invention
The present invention relates generally to electrical switching devices. More particularly the invention relates to an arc chute arrangement for arc quenching in electrical switching devices.
2. Description of Related Art
Conventional Circuit Breaker consists of housing and cover made up of insulating material, pair of separable contacts enclosed within the housing, cover and arc quenching device known as Arc chute. The switching arc in circuit breaker and its motion are determined by the intensity of current, electromagnetic from arc chute as well as the gas-dynamic process within the arc chute.
The arc chute consists of stack of deion plates made up of magnetic material to attract, split-up & cool the arcs. The stack of deion plates is trapped in between two plates known as lining made up of electrically insulating material. The function of deion plates is to split the arc in several series arcs of approximately equal length which will result in higher arc voltage and distinctly greater dielectric strength after current zero.
Some of the prior arts in the related field of invention are as follows:
U.S. Pat. No. 4,375,021 provides a rapid arc extinguishing assembly includes an arc chute comprising a large number of essentially parallel deion plates each in form of thin magnetically permeable, electrically conductive plates bent in U-shape, with the curve of the U facing the circuit breaker contacts and the arms thereof insulated from each other by a thin insulation sheet. To promote arc extinction by the arc chute and accelerated breaker contact separation, the breaker contacts are flanked by a magnetic assembly comprising opposed columns of parallel, spaced ferromagnetic plates embedded in an insulating material. The columns may be magnetically coupled by a yoke to create a closed slot in which the breaker movable contact travels.
US2009255904 provides an arc splitter arrangement for an electrical switch comprises at least two arc splitters composed of a ferromagnetic material disposed parallel to one another, wherein each of the at least two arc splitters has a V-shaped cutout on a narrow face edge forming an inlet area for an arc, and an insulating material at least partially coating at least one side of the arc splitter, wherein the at least one side includes an area located behind the inlet area in an arc running direction, the area being free of, and surrounded by, the insulating material. A service switching device comprises at least one arc splitter arrangement.
In the conventional deion plate construction (single metal plate) the arc root forms on both side of the deion plate, in presented construction of deion plate assembly (ablative material sandwiched between two metal plates) the arc root forms only on one side of the metal plate which results in less erosion of deion plate assembly and hence ensures the faster quenching of arc in subsequent short circuit faults.
The current invention makes use of ablative material (gassing material) near arcing zone in such a way that the electro-negative gasses released by the ablative material absorb the charged particles from arc thereby reducing the intensity of ions in the arcing zone which increase the dielectric strength of the region. With increase in dielectric strength of the arcing region the arc quenching becomes faster.
In conventional arc chute assembly there is possibility that the arc can flash over or re-strike at the end of the deion plate stack or else on the side edges, thus preventing arc voltage build up and correct short circuit disconnection. In conventional arc chute assembly during arc interruption, the molten material gets deposited at the side edges of the deion plate and forms a current path by connecting deion plates by bridging the gap between them at side edges. This current path formed due to molten material reduces the effectiveness of arc quenching process and results in arc flash over or restrike. In presented construction of deion plate assembly, deion plates have a chamfered profile at one corner. The molten material gets deposited at the ends of deion plates and forms conductive bridge between consecutive deion plates. In present construction, the gap between two consecutive edges is twice the gap between two deion plates of conventional arc chute. Thereby the possibility of flash-over arc restrike is minimized. At the same time chamfer profile generates high magnetic field that drive the arc inside arc chute and said chamfered profile arranged alternatively thereby substantially lengthening the arc.
In view of the above disadvantages of the prior art the present inventors have designed the deion plate assembly of the present invention so that it provides faster build up of dielectric strength, due to use of ablative material and higher voltage drop across deion plate assembly, due to the increased length of current path, as compared to conventional deion plates (single metal plate construction) wherein the voltage drop across deion plate depends on the thickness and material used for the deion plate. This invention is related to the arrangement of deion plates used in arc chute of an electrical switching devices such as circuit breaker, a motor circuit breaker or contactor. The deion plate consists of stack assembly of ablative material sandwiched in between two electrically connected metal plates.